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Recruitment Curve (recruitment + curve)
Selected AbstractsSoleus T reflex modulation in response to spinal and tendinous adaptations to unilateral lower limb suspension in humansACTA PHYSIOLOGICA, Issue 3 2008O. R. Seynnes Abstract Aim:, To investigate the influence of tendinous and synaptic changes induced by unilateral lower limb suspension (ULLS) on the tendon tap reflex. Methods:, Eight young men underwent a 23-day period of ULLS. Muscle cross-sectional area (CSA), torque and electromyographic (EMG) activity of the plantar flexor muscles (normalized to the M wave), Achilles tendon,aponeurosis mechanical properties, soleus (SOL) H and T reflexes and associated peak twitch torques were measured at baseline, after 14 and 23 days of ULLS, and 1 week after resuming ambulatory activity. Results:, Significant decreases in muscle CSA (,9%), in maximal voluntary torque (,10%) and in the associated SOL EMG activity (,16%) were found after ULLS (P < 0.05). In addition to a 36% (P < 0.01) decrease in tendon,aponeurosis stiffness, normalized H reflex increased by 35% (P < 0.05). An increase in the slope (28%, P < 0.05) and intercept (85%, P < 0.05) of the T reflex recruitment curve pointed to an increase in the gain and to a decrease in the sensitivity of this reflex, possibly resulting from the decrease in the tendon,aponeurosis stiffness at low forces. Following ULLS, changes in tendinous stiffness correlated with changes in neuromuscular efficiency (peak twitch torque to reflex ratio) at higher tendon tap forces. Conclusion:, These findings point out the dual and antagonistic influences of spinal and tendinous adaptations upon the tendon tap reflex in humans under conditions of chronic unloading. These observations have potential implications for the sensitivity of the short-latency Ia stretch response involved in rapid compensatory contractions to unexpected postural perturbations. [source] Recruitment variability of resident brown trout in peripheral populations from southern EuropeFRESHWATER BIOLOGY, Issue 12 2008GRACIELA G. NICOLA Summary 1. Population regulation was studied for seven consecutive years (1992,98) in five rivers at the periphery of the distribution of Salmo trutta, where the fish were living under environmental constraints quite different from those of the main distribution area. 2. Recruitment is naturally highly variable and the populations had been earlier classified as overexploited. Thus we expected that densities of young trout in most populations would be too low for density-dependent mortality to operate. We tested this by fitting the abundance of recruits to egg densities over seven consecutive years (stock,recruitment relationship), and used the results to judge whether exploitation should be restricted in the interests of conserving the populations. 3. The density of 0+ trout in early September, as well as the initial density of eggs and parents, varied greatly among localities and years. The data for all populations fitted the Ricker stock,recruitment model. The proportion of variance explained by the population curves varied between 32% and 51%. However, in most cases the observations were in the density-independent part of the stock,recruitment curve, where densities of the recruits increased proportionally with egg densities. 4. Our findings suggest that recruitment densities in most rivers and years were below the carrying capacity of the habitats. Although density-dependent mechanisms seemed to regulate fish abundance in some cases, environmental factors and harvesting appeared generally to preclude populations from reaching densities high enough for negative feedbacks to operate. The findings thus lend support to Haldane's (1956) second hypothesis that changes in population density are primarily due to density-independent factors in unfavourable areas and areas with low density due to exploitation. Exploitation should be reduced to allow natural selection to operate more effectively. [source] Decreased cortical inhibition and yet cerebellar pathology in ,familial cortical myoclonic tremor with epilepsy'MOVEMENT DISORDERS, Issue 16 2007Anne-Fleur van Rootselaar MD Abstract Cortical hyperexcitability is a feature of "familial cortical myoclonic tremor with epilepsy" (FCMTE). However, neuropathological investigations in a single FCMTE patient showed isolated cerebellar pathology. Pathological investigations in a second FCMTE patient, reported here, confirmed cerebellar Purkinje cell degeneration and a normal sensorimotor cortex. Subsequently, we sought to explore the nature of cerebellar and motor system pathophysiology in FCMTE. Eye movement recordings and transcranial magnetic stimulation performed in six related FCMTE patients showed impaired saccades and smooth pursuit and downbeat nystagmus upon hyperventilation, as in patients with spinocerebellar ataxia type 6. In FCMTE patients short-interval intracortical inhibition (SICI) was significantly reduced. Resting motor threshold, recruitment curve, silent period, and intracortical facilitation were normal. The neuropathological and ocular motor abnormalities indicate cerebellar involvement in FCMTE patients. Decreased SICI is compatible with intracortical GABAA -ergic dysfunction. Cerebellar and intracortical functional changes could result from a common mechanism such as a channelopathy. Alternatively, decreased cortical inhibition may be caused by dysfunction of the cerebello-thalamo-cortical loop as a result of primary cerebellar pathology. © 2007 Movement Disorder Society [source] Caffeine increases spinal excitability in humansMUSCLE AND NERVE, Issue 3 2003C. Walton MSc Abstract The Hoffman reflex (H reflex) has long been established as a measure of spinal excitability. Caffeine is one of the most widely consumed drugs in the world. Because it is known to increase excitatory neurotransmission, we hypothesized that caffeine would increase spinal excitability and thus alter the H reflex by increasing its amplitude. Seven subjects each attended the laboratory on 2 days. Caffeine (6 mg/kg) was administered on one day and a placebo was administered on the other. The tibial nerve was stimulated at incremental intensities to create an H-reflex recruitment curve prior to capsule administration (pretest) and 1 h later (posttest) on each day. The slope of H-reflex recruitment curve normalized to that of the M wave (Hslp/Mslp) was compared (pretest to posttest). Caffeine increased spinal excitability 43 ± 17% (P < 0.05). Thus, caffeine may be used to safely increase spinal excitability in electrophysiological studies of the human neuromuscular system. Our results also suggest that caffeine intake should be controlled when the H reflex is used in diagnostic and experimental situations. Muscle Nerve 28: 359,364, 2003 [source] The effect of strength training on the force of twitches evoked by corticospinal stimulation in humansACTA PHYSIOLOGICA, Issue 2 2009T. J. Carroll Abstract Aim:, Although there is considerable evidence that strength training causes adaptations in the central nervous system, many details remain unclear. Here we studied neuromuscular responses to strength training of the wrist by recording electromyographic and twitch responses to transcranial magnetic stimulation (TMS) and cervicomedullary stimulation of the corticospinal tract. Methods:, Seventeen participants performed 4 weeks (12 sessions) of strength training for the radial deviator (RD) muscles of the wrist (n = 8) or control training without external load (n = 9). TMS recruitment curves were constructed from stimuli at five to eight intensities ranging between 15% below resting motor threshold and maximal stimulator output, both at rest and during isometric wrist extension (EXT) and RD at 10% and 50% of maximal voluntary contraction (MVC). Responses to weak TMS and cervicomedullary stimulation (set to produce a response of 10% maximal M wave amplitude during 10% MVC EXT contraction) were also compared at contraction strengths ranging from 10% to 75% MVC. Results:, Isometric strength increased following strength training (10.7% for the RD MVC, 8.8% for the EXT MVC), but not control training. Strength training also significantly increased the amplitude of TMS- and cervicomedullary-evoked twitches during low-force contractions. Increases in the force-generating capacity of the wrist extensor muscles are unlikely to account for this finding because training did not affect the amplitude of twitches elicited by supra-maximal nerve stimulation. Conclusion:, The data suggest that strength training induces adaptations that increase the net gain of corticospinal-motor neuronal projections to the trained muscles. [source] | |||||||||||||